Fig. 4 |. Neutron diffraction and inelastic neutron-scattering data.

a, Temperature-subtracted neutron powder diffraction data (330 mK − 1.5 K) collected under 0 T, showing the absence of low-temperature magnetic order. The red line is a constant fit to the subtracted data. b, Under an applied field of 5 T at 450 mK, new magnetic peaks appear at (1/3, 1/3, $z$) positions ($z=0,1,3$), corresponding to an ordering wave vector of $\mathbf{q}=(1/3,1/3,0)$. The data were refined by analysing field-subtracted data (5 T − 0 T), which are constrained by the suppressed (1/3, 1/3, 2) reflection. c, The best fit to the 5 T induced magnetic state using the two-q structure $\mathbf{q}=(1/3,1/3,0)+\mathbf{q}=(0,0,0)$ is generated by a collinear spin structure with Yb moments of $1.36\left(10\right){\mu }_{\mathrm{B}}$. The displayed structure aligns moments approximately along the <1, −1, −1> direction and has six symmetrically equivalent structures generated by three-fold in-plane rotational and mirror symmetries. d, Inelastic neutron-scattering spectrum collected at 67 mK and 0 T. e, Inelastic neutron-scattering spectrum collected at 74 mK and ${\mu }_{0}H=5\mathrm{T}$. f, Linear spin wave calculations showing the powder-averaged $S(Q,E)$ for a two-dimensional triangular lattice of anisotropic ${\mathrm{Y}\mathrm{b}}^{3+}$ moments of NaYbO₂ in a 5 T field and three-sublattice ordering. Error bars denote one standard deviation of the data.